Dual sound reception apparatus in protocetid whales

Modern cetaceans dwell in an underwater world of sound. Due to the specific physico-acoustic conditions inherent in the aquatic environment, sound reception pathway in modern whales drastically differs from that of land mammals and implies deep modification of their external acoustic apparatus. To fathom the implementation of this underwater hearing system, the rare data on the auditory region of early whales are paramount. Among them, previous studies on protocetid auditory region highlighted the presence of two potential acoustic portals on the lateral wall of the bulla: a tympanic ring and a tympanic plate. Through an anatomical survey, I explore the external sound reception apparatus of a protocetid whale and discuss the functionality of these two sound portals. The study of the tympanic ring, allow me to propose a reconstruction of the tympanic membrane of this early whale, suggesting that this structure was functional for aerial hearing. 3D investigation of the bone thickness of the bulla reveals the presence of homologous areas of reduced thickness within the tympanic plate of protocetid and modern cetaceans, highlighting a common functioning of this structure for underwater hearing. Thus, this detailed anatomical survey of the lateral wall of a protocetid tympanic bulla confirms the functionality of the two contiguous acoustic portals and sheds new light on the sound transmission mechanism in these early whales.

Memory-specific correlated neuronal activity in higher-order auditory regions of a parrot

Male budgerigars (Melopsittacus undulatus) are open-ended learners that can learn to produce new vocalisations as adults. We investigated neuronal activation in male budgerigars using the expression of the protein products of the immediate early genes zenk and c-fos in response to exposure to conspecific contact calls (CCs: that of the mate or an unfamiliar female) in three subregions (CMM, dNCM and vNCM) of the caudomedial pallium, a higher order auditory region. Significant positive correlations of Zenk expression were found between these subregions after exposure to mate CCs. In contrast, exposure to CCs of unfamiliar females produced no such correlations. These results suggest the presence of a CC-specific association among the subregions involved in auditory memory. The caudomedial pallium of the male budgerigar may have functional subdivisions that cooperate in the neuronal representation of auditory memory.

Can You Hear Me Now? A Comparative Survey of Pinniped Auditory Apparatus Morphology

Over the past century research on the morphology of the auditory apparatuses of pinnipeds, which include Phocidae (true seals), Otariidae (sea lions and fur seals), and Odobenidae (walruses) is extremely limited, in comparison to other Carnivora. Although, the auditory region and surrounding basicrania are areas that are evolutionarily conservative, most literature is unclear due to mixed terminology, inaccurate information, and indistinct, outdated illustrations. Th e lack of adequate and current studies demonstrates the need for compiling morphological information of the auditory region of modern carnivores in relation to hearing. Auditory terminology will be explored to show morphological comparisons and naming practices among the carnivoran families. By streamlining accurate terminology with straightforward illustrations, the behavioral information gleaned from auditory morphological structures will be clearer even among the diverse members of Carnivora. Th is initial assessment will detail the limited information in prior research on the hearing adaptations for transitional semiaquatic carnivores. Th is preliminary review will help to establish the adaptive patterns (from land to sea) in the basicranial morphology of early pinnipeds, especially in phocids.

Skeletal Anatomy of the Basicranium and Auditory Region in the Metacheiromyid Palaeanodont Metacheiromys (Mammalia, Pholidotamorpha) Based on High-Resolution CT Scans

Cranial skeletal material of the Eocene palaeanodont Metacheiromys marshi was examined using high-resolution CT scans. The present study represents the first time that CT scans have been conducted on skulls of this extinct fossorial mammal. The bony osteology of the auditory region is described in detail, including the ectotympanic and entotympanic, the petrosal in both tympanic and endocranial views, and the middle ear ossicles. The results of this investigation confirm a number of derived resemblances between palaeanodonts and xenarthrans, including a large entotympanic element in the medial wall of the auditory bulla, the presence of an anteroventral process of the tegmen tympani, and a posttemporal canal. However, the present study also provides novel derived auditory features linking palaeanodonts and pangolins, consistent with current understanding of palaeanodont phylogenetic relationships, including the absence of an ectotympanic styliform process, a posterolaterally oriented aperture to the cochlear fossula, and a convex mallear head / concave incudal head. Several autapomorphic features characterizing the auditory osteology of Metacheiromys are also noted. The presence of a large, spherical mallear head, and of a capacious tympanic cavity extended into sinuses in surrounding bones, likely represent adaptations for fossoriality, consistent with palaeobiological inferences drawn from the postcranial anatomy of Metacheiromys.